The invention relates to a hydrodynamic brake including a rotor and a stator in shell form which together define an annular working space, and respective blades on the stator and the motor and projecting into the shell. The invention particularly concerns inlet and outlet of working medium to the space.
Oil is commonly used as a working medium of hydrodynamic brakes such as retarders in motor vehicles. The oil is supplied to the toroidal space defined by the stator and rotor of the retarder. The oil exerts in the toroidal space a braking action on the rotor and hence on the vehicle's driveline which is connected to the rotor. During the resulting braking process, the oil's kinetic energy is converted to thermal energy. Upon leaving the toroidal space, the oil is led via a pipe circuit to a heat exchanger before the cooled oil is led back to the toroidal space. To prevent overheating of the oil it is important to maintain a large flow through the toroidal space. With a large oil flow it is also possible to achieve effective cooling of the retarder in association with the toroidal space by means of the circulating oil. A simple way of achieving a large flow of oil through the toroidal space is to utilise the pressure differences which arise in the toroidal space during the operation of the rotor.
WO 02/04835 corresponding to U.S. Pat. No. 6,918,471, commonly owned herewith, describes advantageous positioning of an inlet and an outlet for the oil in the toroidal space whereby the aforesaid pressure differences are utilised to provide a large oil flow through the toroidal space. To that end, the inlet incorporates a multiplicity of input holes arranged on surfaces of the stator where low pressure occurs during operation of the retarder. The outlet incorporates output holes arranged on surfaces of the stator where relatively high pressure occurs during operation of the retarder. The oil is thus easily led into the toroidal space via the input holes and pushed out at high pressure from the toroidal space via the output holes to the pipe circuit which is intended to recirculate the oil to the toroidal space after cooling. Oil from an oil sump is also supplied continuously to the toroidal space during retarder braking. This entails the oil from the oil sump being pumped up to the high pressure which prevails in the pipe circuit which recirculates the oil to the toroidal space after cooling. The pump is thus subject to severe requirements in that it must have sufficient capacity to impart to the oil from the oil sump at least as high a pressure as the oil in said pipe circuit. Severe requirements also apply in this case to the pipe circuit adjacent to the pump to prevent the occurrence of leakage.